Two-Dimensional Anion-Pillared Metal-Organic Framework for Sieving Separation of Propylene from Propane with Ultrahigh Kinetic Performance.

Adsorptive separation of propylene/propane using porous materials offers a promising alternative to energy-intensive cryogenic distillation. Molecular sieving-type adsorbents are considered the most ideal materials due to their superior selectivity and efficiency, but many suffer from limited adsorption capacity and slow diffusion due to small pore sizes. Here, we present a solvent-blocking strategy on NbOFFIVE-1-Ni (KAUST-7), the inaugural reported metal-organic framework for propylene/propane separation based on molecular sieving. By use of solvents of varying sizes, KAUST-7 with different framework strain energies and crystal morphologies was synthesized. Notably, methanol and ethanol facilitated the formation of well-defined rectangular nanosheets (designated as KAUST-7(MeOH) and KAUST-7(EtOH)), which have a high aspect ratio that shortens mass transfer paths and markedly augments gas diffusion. In comparison to the original sample, KAUST-7(MeOH) exhibits enhanced adsorption kinetics, with the propylene adsorption equilibrium time being curtailed by over 20-fold, along with a significantly enhanced adsorption capacity by 60% to 48 cm3 g-1, while the propane adsorption remains nearly unaltered. Molecular dynamics simulations reveal that methanol inhibits (0 0 2) faces more strongly, leading to faster lateral crystal growth. Its improved adsorption capacity, fast adsorption kinetics and regeneration, and excellent moisture stability make it a promising candidate for industrial application.